16,736 research outputs found
Phononic Josephson oscillation and self-trapping with two-phonon exchange interaction
We propose a bosonic Josephson junction (BJJ) in two nonlinear mechanical
resonator coupled through two-phonon exchange interaction induced by quadratic
optomechanical couplings. The nonlinear dynamic equations and effective
Hamiltonian are derived to describe behaviors of the BJJ. We show that the BJJ
can work in two different dynamical regimes: Josephson oscillation and
macroscopic self-trapping. The system can transfer from one regime to the other
one when the self-interaction and asymmetric parameters exceed their critical
values. We predict that a transition from Josephson oscillation to macroscopic
self-trapping can be induced by the phonon damping in the asymmetric BJJs. Our
results opens up a way to demonstrate BJJ with two-phonon exchange interaction
and can be applied to other systems, such as the optical and microwave systems.Comment: 7 pages, 7 figure
Single-photon nonreciprocal transport in one-dimensional coupled-resonator waveguides
We study the transport of a single photon in two coupled one-dimensional
semi-infinite coupled-resonator waveguides (CRWs), in which both end sides are
coupled to a dissipative cavity. We demonstrate that a single photon can
transfer from one semi-infinite CRW to the other nonreciprocally. Based on such
nonreciprocity, we further construct a three-port single-photon circulator by a
T-shaped waveguide, in which three semi-infinite CRWs are pairwise mutually
coupled to each other. The single-photon nonreciprocal transport is induced by
the breaking of the time-reversal symmetry and the optimal conditions for these
phenomena are obtained analytically. The CRWs with broken time-reversal
symmetry will open up a kind of quantum devices with versatile applications in
quantum networks.Comment: 10 pages, 6 figure
Nonreciprocal conversion between microwave and optical photons in electro-optomechanical systems
We propose to demonstrate nonreciprocal conversion between microwave and
optical photons in an electro-optomechanical system where a microwave mode and
an optical mode are coupled indirectly via two non-degenerate mechanical modes.
The nonreciprocal conversion is obtained in the broken time-reversal symmetry
regime, where the conversion of photons from one frequency to the other is
enhanced for constructive quantum interference while the conversion in the
reversal direction is suppressed due to destructive quantum interference. It is
interesting that the nonreciprocal response between the microwave and optical
modes in the electro-optomechanical system appears at two different frequencies
with opposite directions. The proposal can be used to realize nonreciprocal
conversion between photons of any two distinctive modes with different
frequencies. Moreover, the electro-optomechanical system can also be used to
construct a three-port circulator for three optical modes with distinctively
different frequencies by adding an auxiliary optical mode coupled to one of the
mechanical modes.Comment: 10 pages, 4 figure
Well-Supported versus Approximate Nash Equilibria: Query Complexity of Large Games
We study the randomized query complexity of approximate Nash equilibria (ANE)
in large games. We prove that, for some constant , any randomized
oracle algorithm that computes an -ANE in a binary-action, -player
game must make payoff queries. For the stronger solution
concept of well-supported Nash equilibria (WSNE), Babichenko previously gave an
exponential lower bound for the randomized query complexity of
-WSNE, for some constant ; the same lower bound was shown
to hold for -ANE, but only when .
Our result answers an open problem posed by Hart and Nisan and Babichenko and
is very close to the trivial upper bound of . Our proof relies on a
generic reduction from the problem of finding an -WSNE to the problem
of finding an -ANE, in large games with actions,
which might be of independent interest.Comment: 10 page
Antibunching effect of the radiation field in a microcavity with a mirror undergoing heavily damping oscillation
The interaction between the radiation field in a microcavity with a mirror
undergoing damping oscillation is investigated. Under the heavily damping
cases, the mirror variables are adiabatically eliminated.
The the stationary conditions of the system are discussed. The small
fluctuation approximation around steady values is applied to analysis the
antibunching effect of the cavity field. The antibunching condition is given
under two limit cases.Comment: 5 pages, no figur
Optimal control of population transfer in Markovian open quantum systems
There has long been interest to control the transfer of population between
specified quantum states. Recent work has optimized the control law for closed
system population transfer by using a gradient ascent pulse engineer- ing
algorithm [1]. Here, a spin-boson model consisting of two-level atoms which
interact with the dissipative environment, is investigated. With opti- mal
control, the quantum system can invert the populations of the quantum logic
states. The temperature plays an important role in controlling popula- tion
transfer. At low temperatures the control has active performance, while at high
temperatures it has less erect. We also analyze the decoherence be- havior of
open quantum systems with optimal population transfer control, and we find that
these controls can prolong the coherence time. We hope that active optimal
control can help quantum solid-state-based engineering.Comment: 19 pages, 10 figure
Improving teleportation fidelity in structured reservoirs
Seeking flexible methods to control quantum teleportation in open systems is
an important task of quantum communication. In this paper, we study how the
super-Ohmic, Ohmic and sub-Ohmic reservoirs affect teleportation of a general
one-qubit state. The results revealed that the structures of the reservoirs
play a decisive role on quality of teleportation. Particularly, the fidelity of
teleportation may be improved by the strong backaction of the non-Markovian
memory effects of the reservoir. The physical mechanism responsible for this
improvement are determined.Comment: 5 pages, 5 figures, Comments are welcome. arXiv admin note: text
overlap with arXiv:1208.1655 by other author
Query Tracking for E-commerce Conversational Search: A Machine Comprehension Perspective
With the development of dialog techniques, conversational search has
attracted more and more attention as it enables users to interact with the
search engine in a natural and efficient manner. However, comparing with the
natural language understanding in traditional task-oriented dialog which
focuses on slot filling and tracking, the query understanding in E-commerce
conversational search is quite different and more challenging due to more
diverse user expressions and complex intentions. In this work, we define the
real-world problem of query tracking in E-commerce conversational search, in
which the goal is to update the internal query after each round of interaction.
We also propose a self attention based neural network to handle the task in a
machine comprehension perspective. Further more we build a novel E-commerce
query tracking dataset from an operational E-commerce Search Engine, and
experimental results on this dataset suggest that our proposed model
outperforms several baseline methods by a substantial gain for Exact Match
accuracy and F1 score, showing the potential of machine comprehension like
model for this task.Comment: CIKM 201
Collective modes in a Dirac insulator with short range interactions
We study a Haldane model with nearest neighbor interactions. We find
one-dimensional like collective modes arising due to the interplay of
pseudo-spin and valley degrees of freedom. In the large band gap or moderate
interaction limit, these excitations are low energy modes lying in the band
gap. The dispersion relations are qualitatively different in trivial insulator
phase and Chern insulator phase, thus can be used to identify the topology of
the Haldane model with the bulk property. We also discuss how to detect these
modes in cold atom systems. An abelian gauge theory will emerge when a physical
current-current interaction is introduced to the Haldane model or the Kane-Mele
model.Comment: minor version, a new reference added. Phys. Rev. B (in press
The effect of Large Magellanic Cloud on the satellite galaxy population in Milky Way analogous Galaxies
Observational work have shown that the two brightest satellite galaxies of
the Milky Way (MW), the Large Magellanic Cloud (LMC) and the Small Magellanic
Cloud (SMC), are rare amongst MW analogues. It is then interesting to know
whether the presence of massive satellite has any effect on the whole satellite
population in MW analogues. In this article, we investigate this problem using
a semi-analytical model combined with the Millennium-II Simulation.
MW-analogous galaxies are defined to have similar stellar mass or dark matter
halo mass to the MW. We find that, in the first case, the halo mass is larger
and there are, on average, twice as many satellites in Milky Way analogs if
there is a massive satellite galaxy in the system. This is mainly from the halo
formation bias. The difference is smaller if MW analogues are selected using
halo mass. We also find that the satellites distribution is slightly
asymmetric, being more concentrated on the line connecting the central galaxy
and the massive satellite and that, on average, LMC have brought in 14.7
satellite galaxies with at its accretion, among which 4.5 satellites
are still within a distance of 50kpc from the LMC. Considering other
satellites, we predict that thereare 7.8 satellites with 50kpc of the LMC. By
comparing our model with the early data of Satellites Around Galactic Analogs
(SAGA), a survey to observe satellite galaxies around 100 Milky Way analogues,
we find that SAGA has more bright satellites and less faint satellites than our
model predictions. A future comparison with the final SAGA data is needed.Comment: 9 pages, 10 figures, published in MNRA
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